Transmitter having a phase control loop whose frequency bandwidth is varied in accordance with modulation modes

ABSTRACT

A transmitter adopting a polar loop system including a phase control loop for controlling the phase of a carrier signal outputted from a transmitting oscillator and an amplitude control loop for controlling the amplitude of a transmitting output signal outputted from a power amplification circuit, and designed to be capable of performing transmission using a GMSK modulation mode and transmission using an 8-PSK modulation mode. In the transmitter, the phase control loop is shared as a phase control loop for use in the GMSK modulation mode and a phase control loop for use in the 8-PSK modulation mode. A component similar to any one of components constituting a loop filter is provided in parallel therewith so that the component can be connected or disconnected in accordance with the modulation mode, for example, by use of a switching element.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application relates to subject matters described in the U.S.patent applications being file based on the United Kingdom PatentApplications No. 0212737.1 filed on May 31, 2002, No. 0212725.6 filed onMay 31, 2002, No. 0212723.1 filed on May 31, 2002, No. 0212735.5 filedon May 31, 2002, and No. 0212732.2 filed on May 31, 2002. All of thoseU.S. applications are assigned to the same assignees of the presentapplication.

BACKGROUND OF THE INVENTION

The present invention relates to a technique effective in application toa radio communication system having a phase control loop and anamplitude control loop for phase and amplitude modulation, and moreparticularly relates to a technique effective in application to asemiconductor integrated circuit for communication with a phasedetection circuit and an amplitude detection circuit built in, and to atransmitter such as a cellular phone in which such a semiconductorintegrated circuit for communication has been incorporated.

In the background art, as one of systems of transmitters (mobiletransmitters) such as cellular phones and the like, there is a systemcalled GSM (Global System for Mobile Communication) which has beenadopted in Europe. In this GSM system, a phase modulation system calledGMSK (Gaussian Minimum Shift Keying) is used as its modulation system soas to shift the phase of a carrier signal in accordance withtransmitting data.

Generally, a high frequency power amplification circuit is incorporatedin a transmission-side output portion in a transmitter. Someconventional transmitters using the GSM system adopt a configuration inwhich a bias voltage to the high frequency power amplification circuitis controlled to obtain output power required for a telephone call by acontrol voltage outputted from a circuit called an APC (Automatic PowerControl) circuit generating a control signal for transmitting output onthe basis of a signal from a detector detecting the transmitting outputand a transmitting level requested from a base band LSI.

In recent cellular phones, an EDGE (Enhanced Data Rates for GSMEvolution) system has been proposed. The EDGE system has a dual-modecommunication function in which communication of audio signals isperformed in GMSK modulation while data communication is performed in 3π/8 rotating 8-PSK (Phase Shift Keying) modulation. The 8-PSK modulationcan be regarded as a modulation in which an amplitude shift is furtheradded to a phase shift of a carrier signal in the GMSK modulation. Whileone-bit information is sent per symbol in the GMSK modulation, 3-bitinformation can be sent per symbol in the 8-PSK modulation. Thus,communication can be performed at a higher transmission rate in the EDGEsystem than in the GSM system.

As a method for implementing a modulation system in which the phasecomponent and the amplitude component of a transmitting signal areallowed to carry information respectively, there has been heretoforeknown a system called a polar loop in which a signal to be transmittedis separated into a phase component and an amplitude component, fed backby a phase control loop and an amplitude control loop respectively,synthesized and outputted by an amplifier (for example, “High LinearityRF Amplifier Design” by Kenington, Peter B., p. 162, published by ARTECHHOUSE, INC., 1979).

In a communication system using the GSM system, it will go well if aphase-modulated signal is outputted in accordance with a requestedoutput level. Accordingly, a radio frequency power amplification circuitin the final stage can be operated in the saturation region. On theother hand, in a radio communication system capable of performingtransmission and reception using the EDGE system, a radio frequencypower amplification circuit in the final stage has to be operatedlinearly in the non-saturation region because it is necessary to performamplitude control. However, in a conventional system for driving a radiofrequency power amplification circuit used in a communication systemusing the GSM system, it is difficult to secure linearity requested ofthe radio frequency power amplification circuit in an area of a lowoutput level. On the other hand, according to the polar loop system,there is an advantage that the request for the linearity of the radiofrequency power amplification circuit can be satisfied while the powerefficiency in an area of a low output level can be also improved.

Therefore, the present inventors made investigations on adoption of thepolar loop system in a radio communication system using the EDGE system.As a result, it was found that there was a problem that it was difficultto satisfy requested specifications in the error vector magnitude (EVM)of transmission waveform, the degree of noise suppression, and the like,when the 8-PSK modulation was implemented in the polar loop system.

Specifically, with a broader frequency bandwidth (the width between thecentral frequency of a transmitting carrier signal and a frequency inwhich the open loop gain reaches 0 dB) of the amplitude control loop,EVM is enhanced, and a characteristic called spectral regrowth showingthe degree of waveform distortion is also improved. However, if thebandwidth is broader, there will arise a problem as follows. That is,the attenuation of the amplitude control loop in the reception frequency20 MHz distant from the central frequency of the transmitting carriersignal becomes so small that a sufficient degree of noise suppressioncannot be obtained.

However, of the two feedback loops, particularly the amplitude controlloop has a loop gain varied due to scattering in manufacturing, so thatthe stability of the loop is degraded. It is therefore difficult toobtain a desired output level in a predetermined time. Further, in asystem using the polar loop system, it was found that there was aproblem that when the output control was carried out for the amplitudemodulation in the amplitude control loop, the gain of the amplitudecontrol loop varied so that the phase margin was reduced and hence thestability of the loop was degraded.

When a radio frequency IC for a transmitter capable of performing boththe transmission using a GMSK modulation mode and the transmission usingan 8-PSK modulation mode is configured, each of the feedback loopsrequires a loop filter for limiting the frequency bandwidth of the loop.It was, however, found that it was desired to change the frequencybandwidths of the respective loops between the GMSK modulation mode andthe 8-PSK modulation mode. It was considered at first that a phasecontrol loop for use in the GMSK modulation mode and a phase controlloop for use in the 8-PSK modulation mode were provided separately. Itwas, however, found that there was a problem that such a configurationled to increase of the number of components for constituting the loopfilters having different properties so that the circuit scale increased.

At the beginning of transmitting in the 8-PSK modulation mode, the twofeedback loops, that is, the phase control loop and the amplitudecontrol loop have to be first stabilized. In that case, however, it isdifficult to stabilize the two feedback loops concurrently. It wastherefore considered that the phase control loop was first stabilizedand the amplitude control loop was then stabilized. It was, however,found that there was a problem that the two feedback loops had to bestabilized in a short time in the EDGE system while the GSM system had acomparatively large time margin because only the phase control loop hadto be stabilized.

In the conventional GSM system, an APC circuit generating a controlsignal for transmitting output on the basis of a signal from thedetector detecting the transmitting output and a transmitting levelrequested from the base band circuit has been used as described above.The present inventors hit upon an idea that if the amplitude controlloop provided in the polar loop was used, the APC circuit could beomitted when the GMSK modulation mode was implemented in the GSM systemor the EDGE system. The inventors therefore made investigations on theidea. As a result, it was found that there was a problem as follows.That is, when a loop filter on the amplitude control loop was designedto meet the GMSK modulation mode, the degree of noise suppression in thereception signal frequency band 20 MHz distant from the carrierfrequency became insufficient at the time of operation in the 8-PSKmodulation mode. On the contrary, when the loop filter was designed tomeet the 8-PSK modulation mode, the phase margin of the loop becameinsufficient at the time of operation in the GMSK modulation mode or inthe case where the output of the power amplifier was very small. Thus,the loop was instable, that is, apt to oscillate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a transmitter such as acellular phone having a function to perform phase modulation andamplitude modulation, in which the error vector magnitude oftransmission wavelength and the spectral regrowth can be improved whilethe noise reaching the reception frequency band can be suppressedsufficiently.

Another object of the invention is to provide a technique by which thenumber of components constituting a circuit and the occupied circuitarea and hence the chip size can be reduced in a transmitter adopting apolar loop system having two feedback loops, that is, a phase controlloop and an amplitude control loop.

A further object of the invention is to provide a technique by which thephase control loop can be stabilized in a short time at the start ofoperation in a transmitter adopting a polar loop system having twofeedback loops, that is, a phase control loop and an amplitude controlloop.

A still further object of the invention is to provide a technique bywhich in a transmitter adopting a polar loop system, insufficiency inthe degree of noise suppression in the reception signal frequency bandcan be prevented or lowering in the stability of the amplitude controlloop due to reduction in phase margin of the loop can be prevented byproperties of a loop filter.

The above-mentioned and other objects and novel features of theinvention will be made obvious from the description of thisspecification and the accompanying drawings.

A brief description will be given to the summary of a representative ofthe invention disclosed in this application as follows.

That is, in a transmitter which adopts a polar loop system including aphase control loop for controlling the phase of a carrier signaloutputted from a transmitting oscillator and an amplitude control loopfor controlling the amplitude of a transmitting output signal outputtedfrom a power amplification circuit, and which is designed to be capableof performing transmission using a GMSK modulation mode and transmissionusing an 8-PSK modulation mode, the phase control loop is shared as aphase control loop for use in the GMSK modulation mode and a phasecontrol loop for use in the 8-PSK modulation mode. Thus, the number ofelements constituting a circuit (radio frequency IC) can be reduced, andthe occupied circuit area and hence the chip size per se can be reduced.

In addition, when the phase control loop is shared as a phase controlloop for use in the GMSK modulation mode and a phase control loop foruse in the 8-PSK modulation mode in such a manner, it is desired thatthe frequency bandwidth of the phase control loop is varied inaccordance with the respective modulation modes. To this end, acomponent similar to any one of components constituting a loop filter isprovided in parallel therewith so that the component can be connected ordisconnected in accordance with a modulation mode, for example, by useof a switching element. Thus, the properties of the loop filter on thephase control loop are varied in accordance with the respectivemodulation modes simply by switching the switching element, so that thephase control loop can be set to have an optimum frequency bandwidth.

Table 1 shows a simulation result of error vector magnitude (EVM) when atransmitting circuit adopting a polar loop system was operated in the8-PSK modulation mode while the frequency bandwidth of the phase controlloop and the frequency bandwidth of the amplitude control loop werevaried variously.

TABLE 1 AM Loop Open Loop PM Loop Open Loop Bandwidth (MHz) Bandwidth(MHz) 0.647 1.151 1.8 2.047 3.639 6.467 0.647 5.99 4.84 1.151 2.03 1.381.30 1.29 1.8 2.047 1.64 0.65 0.45 0.42 3.639 1.60 0.51 0.20 0.14 6.4673.69 1.59 0.50 0.16 0.06 (%)

Table 2 shows spectral regrowth (attenuation of signal level of afrequency 0.4 MHz distant from the frequency of a carrier signal)obtained by a simulation carried out in similar conditions.

TABLE 2 AM Loop Open Loop PM Loop Open Loop Bandwidth (MHz) Bandwidth(MHz) 0.647 1.151 1.8 2.047 3.639 6.467 0.647 −46 −42 1.151 −50 −54 −52−51 1.8 2.047 −47 −60 −61 −59 3.639 −46 −58 −69 −68 6.467 −41 −46 −57−69 −73 (dBm/100 kHz)

It is understood from Tables 1 and 2 that the error vector magnitude andthe spectral regrowth are improved as the frequency bandwidths of thephase control loop and the amplitude control loop are made broader. Onthe other hand, Table 3 shows noise obtained by a simulation carried outin similar conditions.

TABLE 3 AM Loop Open Loop PM Loop Open Loop Bandwidth (MHz) Bandwidth(MHz) 0.647 1.151 1.8 2.047 3.639 6.467 0.647 −82.9 −66.6 1.151 −81.11.8 −80.7 2.047 −80.7 −79.8 3.639 −73.3 6.467 −71.0 −65.3 (dBm/100 kHz)

It is understood from Table 3 that the degree of noise suppression isimproved as the frequency bandwidths of the phase control loop and theamplitude control loop are made narrower. From Tables 1 to 3, all theproperties do not satisfy required specifications sufficiently when thefrequency band of the loop is 1.151 MHz, but satisfy the requiredspecifications sufficiently when the frequency band is 2.047 MHz. Thus,in the present invention, the frequency band of the amplitude controlloop in the 8-PSK modulation mode was set to be (the frequency of acarrier signal ±1.8 MHz).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic configuration of atransmitter of a polar loop system according to an embodiment of thepresent invention and a configuration example of a radio communicationsystem using the transmitter;

FIG. 2 is a graph showing the open gain characteristic of a phase loopin the transmitter in FIG. 1;

FIG. 3 is a graph showing the open gain characteristic of an amplitudecontrol loop in the transmitter in FIG. 1;

FIG. 4 is a block diagram showing a more detailed configuration exampleof a polar loop in the transmitter in FIG. 1;

FIGS. 5(A) and 5(B) are graphs showing the relationship between anoutput control voltage VRAMP and the gains of an output power amplifierand a variable gain amplification circuit in the transmitter of a polarloop system according to the invention, and the relationship between theoutput control voltage VRAMP and the output power of the output poweramplifier, respectively;

FIG. 6 is a circuit diagram showing a specific example of the variablegain amplification circuit used in the embodiment of the invention;

FIG. 7 is a circuit diagram showing a specific example of a generalanalog phase detection circuit in the conventional art;

FIGS. 8(A) and 8(B) are graphs showing the relationship between thephase difference between input signals and the output current in theanalog phase detection circuit of FIG. 7;

FIG. 9 is a circuit diagram showing a specific example of a phasedetection circuit used in the embodiment of the invention;

FIG. 10 is a timing chart showing timings of respective signals in thephase detection circuit of FIG. 9;

FIG. 11 is a graph showing the relationship between the phase differencebetween input signals and the output current in the phase detectioncircuit of FIG. 9;

FIGS. 12(A) and 12(B) are graphs showing the open gain characteristicand the phase characteristic of the amplitude control loop in thetransmitter of FIG. 1;

FIG. 13 is a block diagram showing a more detailed configuration exampleof the amplitude control loop when a loop filter on the amplitudecontrol loop has been switched to a load LPF 3 in the transmitter ofFIG. 1;

FIG. 14 is a circuit diagram showing a specific example of an amplitudedetection circuit used in the embodiment of the invention; and

FIG. 15 is a circuit diagram showing a specific example of loop filtersand a switching circuit therefor used in the embodiment of theinvention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a schematic configuration of a transmitter of a polar loopsystem according to an embodiment of the present invention. In FIG. 1, areference numeral 100 represents a radio frequency IC which can performGMSK modulation in a GSM system or 8-PSK modulation in an EDGE system;200, a power module including a radio frequency power amplificationcircuit (hereinafter referred to as “power amplifier”) 210 for drivingan antenna ANT so as to perform transmission, a coupler 220 fordetecting transmitting power, and so on; 300, a base band circuit forgenerating I/Q signals on the basis of transmitting data (base bandsignal) or generating a control signal for the radio frequency IC 100 ora bias voltage V_(BIAS) for the power amplifier 210 in the power module200; TxVCO, a transmitting oscillator for generating a phase-modulatedtransmitting signal (carrier signal), and LPF1, a loop filter forlimiting the bandwidth of a phase control loop.

The radio frequency IC 100 is formed as a semiconductor integratedcircuit on one semiconductor chip. As well as the above-mentionedtransmission-system circuit, a reception-system circuit 190 is alsoformed on the chip of the radio frequency IC 100. The reception-systemcircuit 190 is constituted by a low noise amplifier (LNA), a mixer(Rx-MIX) for down-converting a reception signal directly into a baseband signal, a high-gain programmable gain amplifier (PGA), and so on.The radio frequency IC 100, the transmitting oscillator TxVCO, the loopfilter LPF, and so on, can be mounted on one insulating substrate suchas a ceramic substrate so as to be formed as a module. The polar loop inthis embodiment has two control loops. One is a feedback loop for phasecontrol (hereinafter referred to as “phase loop”) and the other is afeedback loop for amplitude control (hereinafter referred to as“amplitude loop or “AM loop””).

The radio frequency IC 100 constituting the polar loop in thisembodiment includes a phase divider 110 for generating signals whosephases are shifted by 90° from an intermediate frequency oscillationsignal φIF generated by an oscillator IF-VCO; an orthogonal modulator120 for mixing I/Q signals supplied from the base band LSI 300 and thesignals divided by the phase divider 110 respectively so as to performorthogonal modulation; a mixer 131 for mixing a feedback signal from thetransmitting oscillator TxVCO and an oscillation signal φRF from a radiofrequency oscillator RF-VCO so as to down-convert the feedback signalinto a signal of 80 MHz for example; a phase detection circuit 140 fordetecting a phase difference between the output signal from the mixer131 and the output signal from the orthogonal modulator 120; a mixer 132for mixing a detection signal from the coupler 220 for detecting theoutput level of the power amplifier 210 and the oscillation signal φRFfrom the radio frequency oscillator RF-VCO; a feedback-side variablegain amplification circuit MVGA for amplifying the output of the mixer132; an amplitude detection circuit 150 for comparing the amplifiedsignal from MVGA and the output signal from the orthogonal modulator 120so as to detect an amplitude difference; a loop filter LPF2 forgenerating a voltage proportional to the output of the amplitudedetection circuit 150 and limiting the frequency bandwidth of theamplitude loop; a forward-side variable gain amplification circuit IVGAfor amplifying the output of the loop filter LPF2; a voltage to currentconverter VIC; a gain control circuit 160 for controlling the gains ofthe variable gain amplification circuits MVGA and IVGA; a register 170for setting control information, an operation mode, and so on, insidethe chip; a sequencer 180 for supplying timing signals to the respectivecircuits inside the chip on the basis of the setting in the register 170so as to operate the respective circuits in a predetermined ordercorresponding to the set operation mode; and so on.

The amplitude loop is constituted by a loop from the coupler 220 to thepower amplifier 210 through the mixer 132, the variable gainamplification circuit MVGA, the amplitude detection circuit 150, theloop filter LPF2, the variable gain amplification circuit IVGA.

The amplitude loop is called the MAIN loop. Further, in this embodiment,the phase loop is constituted by a loop from the phase detection circuit140 back to the phase detection circuit 140 through the loop filterLPF1, the transmitting oscillator TxVCO and the mixer 131.

This phase loop is called the SUB loop. Specifically, when there occursa phase difference between the output signal from the orthogonalmodulator 120 and the feedback signal from the mixer 131, a voltage toreduce the difference is supplied to the frequency control terminal ofthe transmitting oscillator TxVCO so that the phase of the feedbacksignal from the mixer 131 coincides with the phase of the output signalfrom the orthogonal modulator 120. By this phase SUB loop, control ismade to prevent the phase of the output of the transmitting oscillatorTxVCO from shifting due to the fluctuation of a power supply voltage orthe change of temperature. Incidentally, the amplitude of thetransmitting oscillator TxVCO is constant.

In this embodiment, a change-over switch SW0 is provided for feeding theoutput of the variable gain amplification circuit MVGA back to the phasedetection circuit 140 so that the path from the coupler 220 to thevariable gain amplification circuit MVGA through the mixer 132 can beused as a common feedback path of the amplitude loop and the phase loop.The switch SW0 is switched by the sequencer 180 in accordance with theconditions of the register 170 set from the base band LSI 300.

The output of the power amplifier 210 includes both a phase-modulatedcomponent and an amplitude-modulated component in the EDGE mode. Thus,either the output of the transmitting oscillator TxVCO or the output ofthe power amplifier 210 may be used as a feedback signal to the phasedetection circuit 140 having an output-side phase component. However, atthe beginning of transmission, the output of the power amplifier 210 hasnot yet been started up. It is therefore impossible to lock the phaseloop with a feedback signal from the amplitude loop. On the other hand,the feedback path for the amplitude loop is essential in the EDGEmodulation mode in order to correct the distortions introduced by thepower amplifier. Therefore, once the loop is locked, the amplitude loopmay be shared to block the phase loop in a narrow sense including themixer 131. Thus, the power consumption can be reduced while the phasemodulation can be performed with higher accuracy. Accordingly, in thisembodiment, at the start-up time of output, the switch SW0 is operatedto perform switching of selection of the feedback signal from the phaseSUB loop. Then, once the loop is stabilized, the switch SW0 is switchedto select the feedback signal from the amplitude loop or phase MAINloop.

The loop filter LPF1 on the phase loop is constituted by capacitors C0and C1 and a resistor R1 connected in series with the capacitor C1. Thevalues of the respective capacitors and resistor are determined so thatthe loop filter LPF1 takes a frequency bandwidth with high noisesuppression capability, for example, 1.2 MHz, in consideration of theGMSK modulation mode comprising only phase modulation.

FIG. 2 shows an open loop gain characteristic of the phase loop. In FIG.2, the abscissa designates the frequency in logarithmic scale withreference to a carrier frequency f0, and the ordinate designates thegain. The solid line AA designates the gain characteristic of the phaseloop when the loop gain is set to be 1.2 MHz, and the chain line BBdesignates the gain characteristic of the phase loop when the loop gainis set to be 1.8 MHz. The distances D1 and D2 designate the signalattenuation of the phase loop at a reception signal frequency 20 MHzdistant from the carrier frequency respectively when the loop gain isset to be 1.2 MHz and when the loop gain is set to be 1.8 MHz. It isunderstood from FIG. 2 that the 20 MHz offset noise quantity is smallerwhen the loop gain is set to be 1.2 MHz than when the loop gain is setto be 1.8 MHz, that is, the quantity of a signal disturbing the receiverchannels is lower.

In this embodiment, a resistor R1 is connected in parallel to a seriesconnection of the resistor R2 and a switch SW3. The resistors R1 and R2and the switch SW3 are provided so that the phase loop can be sharedbetween the GMSK modulation mode and the 8-PSK modulation mode. When theswitch SW3 is turned on, the resistor R2 is connected in parallel withthe resistor R1 so that the frequency bandwidth of the loop filter LPF1is extended to be 1.8 MHz. That is, the amplitude loop whose frequencybandwidth is 1.8 MHz is made valid in the 8-PSK modulation mode.Accordingly, when the switch SW3 is turned on, the frequency bandwidthof the loop filter LPF1 is set to be 1.8 MHz identical to the frequencybandwidth of the amplitude loop. Thus, the operation is stabilized.

On the other hand, in the GMSK modulation mode, the amplitude loop whosebandwidth is 1.8 MHz is made invalid. Accordingly, when the switch SW3is turned off, the frequency bandwidth of the loop filter LPF1 is set tobe 1.2 MHz narrower than the frequency bandwidth of the amplitude loopso that the stability of the loop and the noise immune capability can beenhanced. Specifically, when the values of the capacitors C0, C1 and theresistor R1 are 1.5 nF, 12 nF and 30 Ω respectively, and the value ofthe resistor R2 is set to be 56 Ω by way of example, the phase loop canbe set to have the aforementioned desired frequency bandwidth.

In this embodiment, without any limitation, the phase loop filter LPF1(including the resistor R2) is formed as an external circuit attached tothe radio frequency IC 100, while the switch SW3 is formed on the chipof the radio frequency IC 100 together with the modulator 120, the phasedetection circuit 140 and so on. The switch SW3 is switched by thesequencer 180 in accordance with the conditions of the register 170 setfrom the base band LSI 300. Of the components constituting the loopfilter LPF1, the resistors R1 and R2 may be formed on the chip of theradio frequency IC 100 together with the switch SW3. Preferably, thecapacitors C0 and C1 are formed as external components so as to preventthe chip size from increasing.

On the other hand, in GMSK mode it is preferable that the AM loop filterLPF2 on the amplitude loop has a narrow open loop frequency bandwidthfrom the point of view of the stability of the loop and the suppressionof noise as shown in the broken line B in FIG. 3. However, preferably,in EDGE mode the loop bandwidth is wider in order to enhance dot linesvector magnitude (EVM) and improve the spectral regrowth. Accordingly,in this embodiment, the AM loop filter for EDGE comprises two poles atlow frequencies near 7 KHz and 10 KHz respectively, a zero near 0.3 MHzand a pole at the high frequency near 10.8 MHz. In EDGE mode, the openloop bandwidth of the AM loop filter is set near 1.8 MHz. The filter isconstituted by capacitors C2 and C3 and a resistor R3 which is connectedin series with the capacitor C3, and a capacitor 4.

In the amplitude loop including such a higher-order loop filter LPF2,although the amplitude can be controlled with high accuracy, the phasemargin is reduced so that the stability of the AM loop is notinconsistently stable. Therefore, in this embodiment, as shown in FIG.1, a load LPF3 is provided separately from the loop filter LPF2 so as toset the loop to have only one pole at low frequency as a whole, and aswitch SW2 is provided for changing over between the loop filter LPF2and the load LPF3. When high accurate amplitude control is required, theswitch SW2 is switched to the filter LPF2 side so as to operate the loopwith the filter LPF2. When high accurate amplitude control is notrequired, or when the stability of the loop is to be enhancedespecially, the switch SW2 is switched to the load LPF3 side so as tooperate the loop with the load LPF3 while increasing the phase margin,with the result that the loop can be stabilized. This operation will bedescribed later again.

When the transmission circuit in this embodiment operates in the 8-PSKmodulation mode, in the amplitude loop, the output of the poweramplifier 210 is detected by the coupler 220. The detection signal isdown-converted into an intermediate frequency band (IF) by the mixer132, amplified by the variable gain amplification circuit MVGA, andsupplied as a feedback signal SFB to the amplitude detection circuit150. Then, a transmitting signal modulated by the orthogonal modulator120 is compared with the feedback signal SFB by the amplitude detectioncircuit 150 so that an amplitude difference is detected. The amplitudedifference is filtered by the AM loop filter LPF2, amplified by thevariable gain amplification circuit IVGA, filtered by the AM loop filterLPF1 and applied as a control voltage VAPC to the output controlterminal of the power amplifier 210. The amplitude control is thusperformed.

In this embodiment, the power amplifier 210 is constituted by an FET orthe like. A driving voltage (Vdd) proportional to the control voltageVAPC is generated by a voltage control circuit (reference numeral 230 inFIG. 4) provided in the power module 200. The driving voltage is appliedto the drain terminal or the source terminal of the FET. On the otherhand, an appropriate bias voltage VBIAS generated by a not-shown biascircuit is applied to the gate terminal of the power FET.

Here, description will be made of the gain control of the variable gainamplification circuit IVGA on the forward path and the variable gainamplification circuit MVGA on the feedback path.

In cellular phone terminals supporting EDGE or GSM, power control isperformed to increase or decrease output power POUT of a power amplifierto a desired value in a predetermined time. In the polar loop, suchpower control is performed by controlling the gain of the variable gainamplification circuit MVGA. Specifically, the feedback signal to theamplitude detector decreases when the gain of the variable gainamplification circuit MVGA is reduced. Accordingly, the AM loop isreacting by increasing the RF gain GPA (POUT/PIN) of the power amplifierto make the feedback signal coincide with the reference signal from themodulator. Thus, when the MVGA gain is reduced, the output power POUTincreases. When decrease in the output power POUT is desired, the gainof the variable gain amplification circuit MVGA must be increased todecrease the output power POUT. In this embodiment, the gain control ofthe variable gain amplification circuit MVGA is carried out by thecontrol voltage VRAMP from the base band LSI 300. In addition, the rateof decrease or increase of the gain GMVGA of the variable gainamplification circuit MVGA is equal to the rate of increase or decreaseof the RF gain GPA of the power amplifier because of the control of theAM loop.

Accordingly, the change of the gain of the variable gain amplificationcircuit MVGA with respect to the control voltage VRAMP forms arightward-downward straight line as shown by the solid line GMA in FIG.5(A). On the contrary, the change of the gain of the power amplifier 210with respect to the control voltage VRAMP forms a rightward-upwardstraight line as shown by the solid line GPA in FIG. 5(A). In addition,as a result, the output power POUT of the power amplifier 210 increaseslinearly with respect to the control voltage VRAMP as shown in FIG.5(B). The relationship between the output power 210 empowered the dBmand the control voltage VRAMP enpowered in the VRAMP is linear thanks tothe characteristic of the MVGA.

While the reference signal SREF from the modulator 120 is a signalmodulated in 8-PSK so that the amplitude component of the signal varies,control is performed so that the amplitude component of the output powerPOUT of the power amplifier coincides with the reference signal SREF bythe operation of the amplitude control loop. At this time, the outputpower POUT of the power amplifier 210 is kept to be a desired value bythe above-mentioned power control. In such a manner, the polar loopproduces at the output of the power amplifier an amplitude modulationvery similar to the original amplitude modulation of the 8-PSK signalproduced by the modulator 120.

FIG. 4 shows an example of a more detailed configuration of thetransmission circuit to which the polar loop system has been applied. Asshown in FIG. 4, in this embodiment, the phase detection circuit 140 isconstituted by a digital phase comparator DPD, an analog phasecomparator APD, a pair of constant current sources CS11 and CS12controlled by the differential output of the digital phase comparatorDPD, and a pair of constant current sources CS21 and CS22 controlled bythe differential output of the analog phase comparator APD. As will bedescribed later, phase comparison is first carried out by the digitalphase comparator DPD at the beginning of transmission, and then switchedto the analog phase comparator APD so that the phase loop can be lockedat a high speed. Incidentally, the magnitudes of the currents of theconstant current sources CS11 and CS12 controlled by the digital phasecomparator DPD are made equal to each other, and the magnitudes of thecurrents of the constant current sources CS21 and CS22 controlled by theanalog phase comparator APD are made equal to each other. In addition,when the loop filter LPF1 is shared between the digital phase comparatorDPD and the analog phase comparator APD, it is desired that the currentof the constant current source CS11, CS12 controlled by the digitalphase comparator DPD is set to be about 4 times as large as the currentof the constant current source CS21, CS22 controlled by the analog phasecomparator APD.

Charge pumps are constituted by the constant current sources CS11 andCS12 and the capacitors C0 and C1 of the phase loop filter LPF1 and bythe constant current sources CS21 and CS22 and the capacitors C0 and C1of the loop filter LPF1 respectively. A voltage proportional to thephase difference between a modulated signal and a feedback signaldetected by the digital phase comparator DPD or the analog phasecomparator APD is charged into the capacitors C0 and C1. Thetransmitting oscillator TxVCO oscillates in accordance with the chargedvoltage of the capacitors C0 and C1 so as to generate a signal whosephase coincides with the phase of the modulated signal outputted fromthe modulator 120.

Though not shown in FIG. 1, on the feedback path of the phase loop, anattenuator ATT1 for attenuating the output of the transmittingoscillator TxVCO and supplying the attenuated output to the mixer 131 isprovided between the oscillator TxVCO and the mixer 131, and a low passfilter PLPF for eliminating harmonics is provided between the mixer 131and the phase detection circuit 140. On the other hand, on the feedbackpath of the amplitude loop, an attenuator ATT2 is provided between thecoupler 220 and the mixer 132, and low pass filters MLPF1 and MLPF2 foreliminating unnecessary waves or harmonics are provided between themixer 132 and the variable gain amplification circuit MVGA and betweenthe variable gain amplification circuit MVGA and the amplitude detectioncircuit 150 respectively.

In this embodiment, a charge pump CGP and a level shift circuit LVS areprovided in a stage after the variable gain amplification circuit IVGA.The charge pump CGP carries out charging or discharging with thedifferential output of the variable gain amplification circuit IVGA soas to integrate the current output of the variable gain amplificationcircuit IVGA. The level shift circuit LVS shifts the voltage generatedin the charge pump by about 0.6 V in the negative direction. The chargepump CGP is constituted by a pair of current sources IS1 and IS2 and acapacitor C4. The level shift circuit LVS is provided because a voltagedown to 0 V has to be applied as a control voltage to the output powermodule 200 while the charge pump cannot supply 0 V due to the nature ofthe current source IS2.

As described previously, when the switch SW3 is turned off in the GMSKmodulation mode while the switch SW3 is turned on in the 8-PSKmodulation mode to switch the frequency bandwidth of the loop filterLPF1. In that case, the current value of the constant current sourceCS21, CS22 of the analog phase comparator APD is changed simultaneouslybetween the GMSK modulation mode and the 8-PSK modulation mode.Specifically, it is desired that the current value of the constantcurrent source CS21, CS22 is changed so that the value (for example, 3.2mA) in the 8-PSK modulation mode is about twice as large as the value(for example, 1.4 mA) in the GMSK modulation mode.

The frequencies of the transmitting oscillator TxVCO used in the GSMsystem and the DCS system or the PCS system are 900 MHz and 1,800 MHz or1,900 MHz, respectively. Oscillators TxVCO different in sensitivity tothe control voltage from the charge pump may be used. In such a case,the current value of the constant current source CS21, CS22 of theanalog phase comparator APD is changed (so that the value in DCS or PCSis made 0.7 mA which is a half of the value in GSM). When thisembodiment is applied to such a system, it is desired that the currentvalue of the constant current source CS21, CS22 is changed so that thevalue (for example 1.6 mA) in the 8-PSK modulation mode in the DCS orPCS system is about twice as large as the value (for example, 0.7 mA) inthe GMSK modulation mode.

Here, description will be made of the phase detection circuit 140 foruse in the transmission circuit of the polar loop system according tothis embodiment. In this embodiment, as described previously, the phasedetection circuit 140 is constituted by a digital phase comparator DPD,an analog phase comparator APD, a pair of constant current sources CS11and CS12 controlled by the differential output of the digital phasecomparator DPD, and a pair of constant current sources CS21 and CS22controlled by the differential output of the analog phase comparatorAPD. Phase comparison is first carried out by the digital phasecomparator DPD at the beginning of transmission, and then switched tothe analog phase comparator APD so that the phase loop can be locked ata high speed.

At first, the present inventors investigated that an analog phasecomparator APD constituted by a multiplication circuit as shown in FIG.7 was used as the phase detection circuit 140 in the polar loop. Such ananalog phase comparator APD is used in a conventional cellular phone ofa GSM system. FIG. 8(A) shows the relationship between the outputcurrent Iout and the phase difference between input signals in theanalog phase comparator APD of FIG. 7. In FIG. 8(A), the solid linedesignates the waveform of the output current Iout with respect to thephase difference when the frequency of a reference signal SREF isidentical to the frequency of an input signal SFB (feedback signal), andthe chain line designates the waveform of the output current Iout withrespect to the phase difference when the frequency of the input signalSFB is ⅓ of the frequency of the reference signal SREF. In the phaseloop using the circuit of FIG. 7, the loop is locked in respectivepoints where the output Iout takes “0” in FIG. 8(A), that is, the phasedifference is ±90° and ±270°. That is, there are a plurality of lockpoints, and at the same time, there is a fear that the loop may belocked also in undesired cases where the frequency of the input signalSFB is generally (2M+1)/(2N+1) (N and M are integers) of the referencesignal SREF.

In this case, when a constant current source 13 as shown by the brokenline is provided in the analog phase comparator APD of FIG. 7 so as toshift the output current lout as a whole as shown in FIG. 8(B), it ispossible to avoid the lock of the loop at undesired frequencies.However, in spite of such a countermeasure, the analog phase comparatorof FIG. 7 has still a disadvantage that the loop is locked at aplurality of points. In addition, the phase range where the lock can bedone is narrow, and the time required for locking (lock up time) isdetermined by the output current lout and the capacitance values of thecapacitors C0 and C1 of the loop filter LPF1. In addition, the lock uptime of the analog phase comparator APD is long to be several hundredsof μsec. Thus, it was found that the lock up time of 10 μsec or shorterrequired in the EDGE system could not be attained at all.

In this embodiment, therefore, the phase detection circuit 140 isconstituted by a digital phase comparator DPD and an analog phasecomparator APD as shown in FIG. 9. The digital phase comparator DPD isoperated earlier, so that the phase loop can be locked at a high speed.

The digital phase comparator DPD is constituted by buffers BFF11 andBFF12, D-type flip-flops FF1 and FF2, a NAND gate G1, and an AND gateG2. The buffers BFF11 and BFF12 have differential inputs and a singleoutput, and receive differential input signals SFB and /SFB andreference signals SREF and /SREF as their inputs, respectively. TheD-type flip-flops FF1 and FF2 carry out latch in response to the buffersBFF11 and BFF12, respectively. The NAND gate G1 receives, as its inputs,the outputs of the flip-flops FF1 and FF2. The AND gate G2 receives, asits inputs, the output of the NAND gate G1 and an activation signalDPD_ON.

It is desired that each of the buffers BFF11 and BFF12 is a circuithaving a function as a limiter for shaping the sine waveform of inputsignals so as to output the signals as square waves. As soon as theactivation signal DPD_ON is set at a high level, the digital phasecomparator DPD starts the phase comparison operation so that theflip-flops FF1 and FF2 carry out latch in response to the rising of theoutputs of the buffers BFF11 and BFF12. Thus, both the outputs of theflip-flops FF1 and FF2 change into a high level. Then, when both theoutputs of the two flip-flops FF1 and FF2 reach the high level, theflip-flops FF1 and FF2 are reset through the NAND gate G1.

As a result, the output pulse width of an earlier-phase one of theflip-flops FF1 and FF2 is broader than the output pulse width of theother. Thus, the current of the current source CS11 or CS12 is made tomore flow correspondingly to this broader pulse width. Accordingly, thecharging voltages of the capacitors C0 and C1 of the loop filter LPF1are changed so that the control voltage to the transmitting oscillatorTxVCO is changed. Thus, the phase of the output of the transmittingoscillator TxVCO is advanced or delayed. When the phase of the inputsignal SFB coincides with the phase of the reference signal SREF, thecharging current of the current source CS11 balances with the chargingcurrent of the current source CS12 so that the charging voltages of thecapacitors C0 and C1 of the loop filter LPF1 are constant and locked.

At this time, as shown by the chain line in FIG. 11, when the phasedifference is −360°, 0° or 360°, the output current Iout becomes “0” sothat the digital phase comparator DPD is locked. When compared withFIGS. 8(A) and 8(B) showing the output current waveform of the analogphase comparator APD, it is understood that the digital phase comparatorDPD has a phase pull-in range of 720° which is wider than the phasepull-in range of 180° in the analog phase comparator APD. In addition,since the digital phase comparator DPD has one lock point, there is nofear of causing imaginary lock. Thus, when the phase pull-in of the loopis carried out first by this digital phase comparator DPD, the pull-incan be carried out at a high speed (8 μsec or shorter).

As described previously, a shoot-through current based on the chargecurrent of the current source CS11 and the discharge current of thecurrent source CS12 flows in the digital phase comparator DPD when thephases coincide with each other. Thus, spurious noise occurs in theoutput of the transmitting oscillator TxVCO due to this shoot-throughcurrent. Consequently, control signals DPD_ON and APD_ON are generatedat the timings as shown in FIG. 10, so that switching to the analogphase comparator APD is carried out after the phase is locked by thedigital phase comparator DPD. Thus, the lock up time can be shortenedwhile avoiding noise generation at the time of transmission andreception. The control signals DPD_ON and APD_ON can be supplied fromthe sequencer 180 shown in FIG. 1.

The analog phase comparator APD is constituted by buffers BFF21 andBFF22, and a multiplication circuit MLT. The buffers BFF21 and BFF22have differential inputs and differential outputs, and receive thedifferential input signals SFB and /SFB and the reference signals SREFand /SREF as their inputs respectively. The multiplication circuit MLTreceives the outputs of the buffers BFF21 and BFF22 as its inputs.Preferably, the buffer BFF21 is a circuit having a function as a limiterfor shaping the sine waveform of the input signals SFB and /SFB so as tooutput the signals as square waves.

The multiplication circuit MLT is constituted by differential twintransistors Q1 and Q2 whose bases receive the differential output of thebuffer BFF21; a constant current source CS0 connected to a commonemitter of the transistors Q1 and Q2; differential twin transistors Q3and Q4 whose common emitter is connected to the collector of thetransistor Q1 and whose bases receive the differential output of thebuffer BFF21; differential twin transistors Q5 and Q6 whose commonemitter is connected to the collector of the transistor Q2 and whosebases receive the differential output of the buffer BFF21; a transistorQ7 connected between the collector of the transistor Q3 and a powersupply voltage Vcc; a transistor Q8 connected between the collector ofthe transistor Q6 and the power supply voltage Vcc; a transistor Q9connected to the transistor Q7 so as to form current mirrors; and atransistor Q10 connected in series with the transistor Q9. Then, thetransistor Q8 and a transistor Q11 as the constant current source CS21of the charge pump are connected to form current mirrors. In addition,the transistor Q10 and a transistor Q12 as the constant current sourceCS22 of the charge pump are connected to form current mirrors.

When the constant current source CS0 is activated in an ON state by thecontrol signal APD_ON, this analog phase comparator APD is activated tostart comparing a phase difference between the input signal SFB and thereference signal SREF and output a current Iout proportional to thephase difference as shown by the solid line in FIG. 11. Here, if acomparison is made between the output current characteristic (solidline) of the analog phase comparator APD and the output currentcharacteristic (broken line) of the digital phase comparator DPD asshown in FIG. 11, the phase lock occurs in the digital phase comparatorDPD when the phase difference is zero, and the phase lock occurs in theanalog phase comparator APD when the phase difference is ±90°.

From this reason, even if switching to the analog phase comparator APDis carried out after the phase of the loop is locked by the digitalphase comparator DPD, the phase is always locked again(resynchronization) by the analog phase comparator APD with the phaseshifted by 90° after the switching. However, since the time required forthis resynchronization is not longer than 1 μsec, it hardly matters. Inaddition, there is a fear that the control voltage for the transmittingoscillator TxVCO may fluctuate slightly. If the time required for theresynchronization or the fluctuation of the VCO control voltage isconcerned, for example, a phase shifter for shifting the phase by 90°may be provided at a place shown by the broken line PSF in FIG. 9, so asto shift by 90° the phases of the reference signals SREF and /SREFsupplied to the digital phase comparator DPD.

Thus, as shown by the chain line in FIG. 11, the output currentcharacteristic of the digital phase comparator DPD is shifted so thatthe phase lock point in the digital phase comparator DPD can be matchedwith the phase lock point in the analog phase comparator APD. Thus, thedelay at the time of switching or the fluctuation of the control voltagecan be prevented. Incidentally, the phase shifter may be provided not onthe input side of the digital phase comparator DPD but on the input sideof the analog phase comparator APD.

Next, description will be made in detail of the configuration andoperation of the amplitude loop in the transmission circuit of the polarloop system according to this embodiment.

In this embodiment, as described previously, from the point of view oftrade-off between improvement in the stability of the amplitude loop andthe suppression of noise, and improvement in the error vector magnitudeand the spectral regrowth, a filter which is constituted by capacitorsC2 and C3 and a resistor R3 connected in series with the capacitor C3and which has two poles and zero as shown by the solid line A in FIG. 3is used as the loop filter LPF2 on the amplitude loop in order to setthe open loop frequency bandwidth of the amplitude loop 1.8 MHz wide.

In the amplitude loop including such a high-order loop filter LPF2having a low frequency, one zero and one pole of high frequency,although amplitude control can be carried out with high accuracy, thephase margin depends on the open loop gain. Therefore, in thisembodiment, as shown in FIG. 13, a load LPF3 is provided separately fromthe loop filter LPF2 so as to set the loop to have only one lowfrequency pole as a whole, and a switch SW2 is provided for changingover between the loop filter LPF2 and the load LPF3. When high accurateamplitude control is required, the switch SW2 is switched to the filterLPF2 side so as to operate the loop with the filter LPF2. When highaccurate amplitude control is not required, or when the stability of theloop is required especially, the switch SW2 is switched to the load LPF3side so as to operate the loop with the load LPF3 while increasing thephase margin. Thus, the loop can be stabilized.

As a result, when the load LPF3 is used to correct the scattering of theloop gain caused by scattering in manufacturing, the phase margin isincreased to stabilize the loop and hence to facilitate calibration. Onthe contrary, when high accurate amplitude control is required, forexample, in the 8-PSK modulation mode, the loop filter LPF2 is used toenhance the error vector magnitude or to improve the spectral regrowth.In the amplitude loop provided with the load LPF3, as describedpreviously, a charge pump CGP constituted by current sources IS1 and IS2and a capacitor C4 also having a function as a loop filter is providedin a stage after the variable gain amplification circuit IVGA.Therefore, the load LPF3 can be constituted by only a resistor RT1.

In the radio frequency IC according to this embodiment, the load LPF3 isused to control the gains of the variable gain amplification circuitsIVGA and MVGA of the amplitude loop in accordance with the outputcontrol voltage VRAMP from the base band LSI 300 so that the outputcontrol voltage VAPC supplied to the power module 200 is generated.Thus, an APC circuit which has been required in the background-art GSMsystem, for detecting the output level and controlling the output of thepower amplifier 210 can be omitted. This reason is as follows. When theamplitude loop is used in the GMSK modulation mode, amplitude modulationis not necessary. Thus, the stability of the amplitude loop is higherthan that in the 8-PSK modulation mode. The GMSK mode has to cover ahigher range of output powers (+33 dBm in GSM, +30 dBm in DCS) than theEDGE mode. At the highest power levels, the noise in the receive band isalso amplified. It is therefore desired that the loop bandwidth is setto be, for example, 200 kHz, narrower than the aforementioned bandwidth1.8 MHz of the amplitude loop in the 8-PSK modulation mode. Accordingly,as the loop filter, the load LPF3 for setting the loop to have only onelow frequency pole as a whole is preferred to the filters LPF2 and LPF4having two low frequency poles one zero and a high frequency pole.

FIGS. 12(A) and 12(B) show the open loop frequency characteristic of theamplitude loop when the loop filter LPF2 is used. Of them, FIG. 12(A)shows the gain characteristic of the amplitude loop, while FIG. 12(B)shows the phase characteristic of the amplitude loop. PM0 to PM2designates phase margins. Reduction in phase margin is a problem becauseit spoils the stability of the amplitude loop. The open loop gain GAMOPof the amplitude loop fluctuates up and down in accordance with thefluctuation of the gain GMVGA of the variable gain amplification circuitMVGA. At this time, the phase of the loop hardly changes. Thus, thephase margin at PM1 or PM2 is reduced in comparison with PMO where thegain of the variable gain amplification circuit MVGA has no fluctuation.

In this embodiment, this problem is solved by controlling the variablegain amplification circuit IVGA on the forward path and the variablegain amplification circuit MVGA on the feedback path so that the sum(GIVGA+GMVGA) of gains GIVGA and GMVGA of the variable gainamplification circuits IVGA and MVGA becomes constant as shown in FIG.5(A). That is, when the gain of the variable gain amplification circuitMVGA on the feedback path is changed to increase (decrease) so as tocontrol the output power POUT of the power amplifier, the gain of thevariable gain amplification circuit IVGA on the forward path isdecreased (increased) in the opposite way to the increase (decrease) ofthe gain of the variable gain amplification circuit MVGA. Thus, the openloop characteristic of the amplitude loop is kept so constant that thephase margin can be prevented from being reduced. For example, when thevariable gain amplification circuit MVGA is constituted by a circuit asshown in FIG. 6, the bias current IEE thereof is changed exponentiallyso that the gain can be controlled to change linearly with respect tothe control voltage VRAMP.

On the other hand, when amplitude modulation is unnecessary, forexample, in the GMSK modulation mode, a low-order filter such as theload LPF3 which can make the bandwidth narrow enough to enhance noisesuppression capability in the reception signal frequency band 20 MHzdistant from the carrier frequency is preferred because the frequencybandwidth of the amplitude loop is not necessarily extended to enhancethe error vector magnitude as shown in FIG. 12(A). In this embodiment,the load LPF3 has a frequency characteristic as shown by the broken lineB in FIG. 3. The resistance value of the resistor RT1 is set so that theopen loop frequency bandwidth of the amplitude loop is about 200 kHz.Because there is only one low frequency pole in the amplitude loop usingthe load LPF3, the phase never turns over 90°. Thus, the stability ofthe loop is guaranteed. Accordingly, when the load LPF3 and thechange-over switch SW2 are provided separately from the loop filter LPF2as in this embodiment, and the amplitude loop using the load LPF3 isused in the GMSK modulation mode, an APC circuit can be omitted, and theradio frequency IC according to this embodiment can be used in a GSMsystem. The switch SW2 is switched by the sequencer 180 in accordancewith the conditions of the register 170 set from the base band LSI 300.

As shown in FIG. 13, the amplitude detection circuit 150 is constitutedby a limiter LMT1 for shaping the waveform of the reference signal SREFfrom the modulator 120; a multiplier MLT1 for generating a signalobtained by multiplying a rectangular wave produced by the limiter LMT1by the reference signal SREF; a current source IS10 controlled by theoutput of the multiplier MLT1; a limiter LMT2 for shaping the waveformof the feedback signal SFB from the amplitude loop; a multiplier MLT2for generating a signal obtained by multiplying a rectangular waveproduced by the limiter LMT2 by the feedback signal SFB; and a currentsource IS20 controlled by the output of the multiplier MLT2. Then, acharge pump is constituted by the current sources IS10 and IS20 and theloop filter LPF2 or the load LPF3, so that a voltage proportional to theamplitude difference between the reference signal SREF and the feedbacksignal SFB is supplied from the loop filter LPF2 or the load LPF3 to thevariable gain amplification circuit IVGA.

FIG. 14 shows a more specific circuit example of the amplitude detectioncircuit 150. The multipliers MLT1 and MLT2 are designed similarly to themultiplier MLT constituting the analog phase comparator ADP shown inFIG. 9. In the stages following the multipliers MLT1 and MLT2, currentmirror circuits and current subtraction circuits CSB1 and CSB2 areprovided for carrying out subtraction on the currents of these currentmirror circuits to thereby supply currents IOUT1 and IOUT2 proportionalto the amplitude difference between the reference signal SREF and thefeedback signal SFB to current output terminals OUT1 and OUT2,respectively. The current subtraction circuit CSB1 is provided for theloop filter LPF2, and the current subtraction circuit CSB2 is providedfor the load LPF3.

Specifically, a current of a transistor Tr17 is copied into a transistorTr19 (Tr30) while a current of a transistor Tr28 is copied into atransistor Tr24 (Tr34) so as to be added thereto, and further copiedinto a transistor Tr22 (Tr32) as a current mirror. On the other hand, acurrent of a transistor Tr18 is copied into a transistor Tr21 (Tr31),and a current of a transistor Tr27 is copied into a transistor Tr29(Tr33) so as to be added thereto. The current of the current mirrortransistor Tr22 (Tr32) is subtracted from this additional current sothat a current IOUT1 (IOUT2) proportional to the amplitude differencebetween the reference signal SREF and the feedback signal SFB issupplied to the current output terminal OUT1 (OUT2).

The current mirror transistor Tr21 of the current subtraction circuitCSB1 and the current mirror transistor Tr31 of the current subtractioncircuit CSB2 correspond to the current source IS10 in FIG. 13. Thecurrent mirror transistor Tr22 of the current subtraction circuit CSB1and the current mirror transistor Tr32 of the current subtractioncircuit CSB2 correspond to the current source IS20 in FIG. 13. In such amanner, the current subtraction circuits CSB1 and CSB2 and the outputterminals OUT1 and OUT2 are provided for the loop filter LPF2 and theload LPF3 separately so that the loop gains using the respective filterscan be optimized independently of each other. In the embodiment of FIG.14, the required gain using the filter LPF2 can be optimized by settingthe emitter size ratio between the transistors Tr17 and Tr19 while therequired gain using the load LPF3 can be optimized by setting theemitter size ratio between the transistors Tr17 and Tr30. In addition,the output impedance of the circuit can be optimized by adjusting thevalue of the emitter resistances of the transistors Tr19 and Tr30.

FIG. 15 shows a specific example of the loop filter LPF2, the load LPF3and their peripheral circuits. In FIG. 15, the reference sign P0represents an external terminal provided in the radio frequency IC 100.The capacitors C2 and C3 and the resistor R3 constituting the loopfilter LPF2 are connected to the external terminal P0. That is, in thisembodiment, the capacitors C2 and C3 and the resistor R3 constitutingthe loop filter LPF2 are connected as external components. On the otherhand, the resistor RT1 constituting the load LPF3 is formed as aninternal component on the chip of the radio frequency IC 100. If thecapacitors are formed on a semiconductor chip in the existing processtechnology, the chip area will increase. Therefore, when the capacitorsare thus formed as external components as described above, the chip sizeof the radio frequency IC 100 can be restrained from increasing.

The switch SW2 for changing over between the loop filters LPF2 and theload LPF3 is constituted by a pair of on-off switches. Either the filteror the load is connected to the output terminal (the current outputterminal OUT1 or OUT2 in FIG. 14) of the amplitude detection circuit 150in accordance with a filter selection signal TP1 or TP2. Switches SW21,SW22, SW31 and SW32 are reset switches respectively. Each switch iscontrolled by an inverted signal /TP1, /TP2 of the selection signal TP1,TP2 so as to be turned on when the filter LPF2 or the load LPF3 is notused. Then, an internal node in each switch is fixed to the groundpotential and prevented from floating. Further, current sources I21 toI23 and I31 to I33 turned on/off by the selection signals TP1 and TP2are provided in the filter LPF2 and the load LPF3, respectively. Currentsources on the side of a filter selected by the change-over switch SW2are turned on concurrently.

An output emitter follower transistor Q21 or Q31 of the filter LPF2 orthe load LPF3 is driven by a voltage generated in the capacitors C2 andC3, a wiring parasitic capacitor, and so on, as a result of theintegration of the output currents from the current sources IS21 andIS22 or IS31 and IS32 of the amplitude detection circuit 150 in thepre-stage. Thus, a signal supplied to one of the input terminals of thevariable gain amplification circuit IVGA in the post-stage is generated.A signal supplied to the other input terminal of the variable gainamplification circuit IVGA is generated as a reference signal at aconstant level by an output emitter follower transistor Q22 (Q32) drivenby a bias voltage (corresponding to two stages of forward voltages ofdiodes) from a bias circuit constituted by a current source I23 (I33)and diodes D21 and D22 (D31 and D32). In the load LPF3, an outputcurrent IOUT2 proportional to the difference between the currents fromthe current sources IS31 and IS32 in the pre-stage is applied to theresistor RT1. Thus, the base potential of the output emitter followertransistor Q31 is biased to a potential higher than the base potentialof the other transistor Q32 by IOUT2·RT1.

Switches SW20 and SW30 are provided between the base terminals of theoutput transistors Q21 and Q22 and between the base terminals of theoutput transistors Q31 and Q32, respectively. When the output of theamplitude detection circuit 150 is not used, the switches SW20 and SW30are turned on to set the potential difference between the differentialinputs of the variable gain amplification circuit IVGA in the post-stageto be “0”. The switches SW20 to SW22 and SW30 to SW32 are controlled bythe sequencer 180 in accordance with the conditions of the register 170set from the base band LSI 300.

Although the invention made by the present inventors has been describedabove specifically along with its embodiment, the invention is notlimited to the embodiment. Not to say, the invention can be modifiedvariously without departing from the spirit and the scope of theinvention.

For example, the above embodiment has described the case where, inaddition to the loop filter LPF2 required to control the amplitude loopwith a frequency bandwidth optimum for 6-PSK modulation there is also aload LPF 3 to allow the amplitude loop to operate with a narrowerfrequency bandwidth and either the filter LPF2 or the load LPF3 isselected by a switch in accordance with required control accuracy. Theload LPF3 may be utilized to calibrate the output power of thetransmitter with respect to the control signal VRAMP before the start-upof the system. When the output power is to be measured for calibration,the output power cannot be measured accurately if the loop is notstable. Thus, by switching the loop filter in the amplitude loop asdescribed above, the output power of the transmitter can be measured inthe state where the loop is stable.

In the above embodiment, the switch SW3 provided in the loop filter LPF1and for changing the frequency bandwidth of the phase loop in accordancewith the modulation mode is provided between the resistor R2 and theground contact. However, the switch SW3 may be provided between theresistor R2 and the connection node between the capacitor C1 and theresistor R1 constituting the loop filter LPF1. Instead of switching theresistors, a design may be done so that capacitors are switched tochange the frequency bandwidth.

Description has been made of the case where the present invention hasbeen applied to a dual band system designed to be able to makecommunication according to two systems, that is, a GSM system and a DCS1800 system. However, the invention may be applied to a system designedto be able to make communication according to either of the GSM systemand the DCS system, or a triple band system designed to be able to makecommunication according to a PCS (Personal Communications System) 1900system in addition to those GSM and DCS systems. According to theinvention, communication with phase modulation in the 8-PSK modulationmode as well as in the GMSK modulation mode can be carried out in such asystem.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A transmitter comprising: a phase control loop for controlling aphase of a carrier signal outputted from a transmitting oscillator; andan amplitude control loop for controlling an amplitude of a transmittingoutput signal outputted from a power amplification circuit whichreceives and amplifies said carrier signal, wherein said transmitter hasa first modulation mode for phase modulation only, using said phasecontrol loop; and a second modulation mode for both phase and amplitudemodulation using both of said phase control loop and said amplitudecontrol loop, so that said phase control loop is shared by said firstmodulation mode and said second modulation mode.
 2. A transmitteraccording to claim 1, wherein a frequency bandwidth of said phasecontrol loop for use in said second modulation mode is identical to afrequency bandwidth of said amplitude control loop for use in saidsecond modulation mode.
 3. A transmitter according to claim 1, wherein afrequency bandwidth of said phase control loop for use in said firstmodulation mode is set to be narrower than a frequency bandwidth of saidphase control loop for use in said second modulation mode and afrequency bandwidth of said amplitude control loop.
 4. A transmitteraccording to claim 1, wherein: said phase control loop includes acarrier signal detection means for detecting said carrier signaloutputted from said transmitting oscillator, a phase detection circuitfor detecting a phase difference between an output of said carriersignal detection means and a signal modulated by a modulator, and a loopfilter for generating a voltage in accordance with said phase differencedetected by said phase detection circuit, so that oscillation of saidtransmitting oscillator is controlled by said voltage generated by saidloop filter, wherein said frequency bandwidth of said phase control loopis set by components of said loop filter.
 5. A transmitter according toclaim 1, wherein said phase detection circuit includes a digital phasedetection circuit and an analog phase detection circuit, and whereinsaid phase control loop is pulled in by said digital phase detectioncircuit first at a start of transmission, and then a phase of said phasecontrol loop is locked by said analog phase detection circuit before orafter a start of power amplification.
 6. A transmitter according toclaim 5, wherein a phase shifter for shifting by 90 degrees either aphase of a feedback signal or a phase of a signal from a modulator isprovided in a stage before either of said digital phase detectioncircuit and said analog phase detection circuit.
 7. A transmitteraccording to claim 1, wherein said amplitude control loop includes:output power detection means for detecting said transmitting outputsignal outputted from said power amplification circuit; an amplitudedetection circuit for detecting an amplitude difference between afeedback signal detected by said output power detection means and saidsignal modulated by a modulator; a second loop filter for holding avoltage proportional to said amplitude difference detected by saidamplitude detection circuit; a first variable gain amplification circuitprovided on a feedback path between said output power detection meansand said amplitude detection circuit and for amplifying said signaldetected by said output power detection means; and a second variablegain amplification circuit provided on a forward path between saidsecond loop filter and said power amplification circuit; and wherein: again of said first variable gain amplification circuit is set inaccordance with an output control voltage in said second modulation modewhile a gain of said second variable gain amplification circuit iscontrolled inversely to that of said first variable gain amplificationcircuit.
 8. A transmitter according to claim 7, wherein said second loopfilter includes a first filter for providing a frequency bandwidthrequired in said second modulation mode, a second filter for providing afrequency bandwidth narrower than said frequency bandwidth determined bysaid first filter, and switching means for selecting either said firstfilter or said second filter, wherein said second loop filter provides afrequency bandwidth for said amplitude control loop, and wherein saidpower amplification circuit is arranged to be controlled in accordancewith said output control voltage in said first modulation mode by saidamplitude control loop which has said second filter connected as saidsecond loop filter.
 9. A transmitter according to claim 7, wherein saidphase control loop includes a carrier signal detection means fordetecting said carrier signal outputted from said transmittingoscillator; and wherein said transmitter further comprises: switchingmeans for selecting either said signal detected by said carrier signaldetection means or said signal detected by said output power detectionmeans, as a feedback signal to said phase detection circuit.
 10. Atransmitter according to claim 1, further comprising switching means forswitching components of a loop filter determining a frequency bandwidthof said phase control loop in accordance with said modulation modes. 11.A transmitter comprising: a semiconductor integrated circuit having abase band circuit for generating I and Q signals in accordance withtransmitting data; a transmitting oscillator for generating a carriersignal; a power amplification circuit for amplifying said carrier signaloutputted from said transmitting oscillator; transmitting output powerlevel detection means for detecting a level of a signal outputted fromsaid power amplification circuit; and a semiconductor integrated circuitfor modulation including an orthogonal modulator for modulating said Iand Q signals onto said carrier signal so as to form an oscillatingsignal of a predetermined frequency, a phase control loop forcontrolling a phase of said carrier signal outputted from saidtransmitting oscillator, an amplitude control loop for controlling anamplitude of a transmitting output signal outputted from said poweramplification circuit, a first variable gain amplification circuitprovided on a feedback path between said transmitting output power leveldetection means and an amplitude detection circuit, and a secondvariable gain amplification circuit provided on a forward path betweensaid amplitude detection circuit and said power amplification circuit;wherein said transmitter has a first modulation mode and a secondmodulation mode, and wherein said phase control loop is shared by saidfirst modulation mode and said second modulation mode.
 12. A transmitterfor generating a modulated carrier signal, comprising: a first operatingmode which modulates a phase component and an amplitude component of acarrier signal, and a second operating mode which modulates a phasecomponent, but not an amplitude component, of said carrier signal; afirst control loop for controlling amplitude and a second control loopfor controlling phase in said first operating mode; wherein said firstcontrol loop is used for the acquisition of a phase lock in said firstoperating mode at the start-up time of output of said transmitter, andwherein said second control loop is used to control the phase of themodulated carrier signal in said second operating mode, and in saidfirst operating mode before the start-up time of output of saidtransmitter.
 13. A transmitter for emitting a modulated carrier signal,said transmitter having a first operating mode in which the phase andthe amplitude of the carrier signal are modulated, a second operatingmode in which only the phase of the carrier signal is modulated, and acontrol loop for controlling the modulation of the carrier signal,wherein said control loop comprises processing means for controlling thephase of the carrier signal, and said processing means is used for phasemodulation control in both of said first operating mode and said secondoperating mode.